Primary hepatic diffuse large B- cell lymphoma mimicking cholangiocarcinoma

Primary lymphoma of liver is a rare malignancy with non-specific clinical features and tumor markers. The presentation and imaging features may be indistinguishable from other hepatic malignant lesions. Pathological diagnosis is the gold standard, and early detection is essential to choose the treatment modality. Here, we share an interesting case of Primary Diffuse Large B cell lymphoma of liver and its imaging findings on Computed tomography (CT), Magnetic Resonance Imaging (MRI) and F-18 FDG PET/CT.


Introduction
Hepatic lymphoma is more commonly secondary in nature due to systemic lymphoproliferative involvement.The Primary hepatic lymphoma is a rare disease that should be considered in the differential diagnosis of other primary hepatic malignancies, particularly cholangiocarcinoma, on cross-sectional imaging (Memeo et al. 1999).With this case, we share the imaging findings of this rare primary liver malignancy and highlight the pivotal role of F-18 FDG (2-fluoro 2-deoxy D glucose) PET/CT (positron emission tomography/ computed tomography) in its diagnosis.
negative.Hepatic enzymes were raised with serum aspartate aminotransferase (AST), alanine transaminase (ALT) and alkaline phosphatase (ALP) being 86 U/l, 110 U/l and 152 U/l respectively.Serum lactate dehydrogenase was also elevated (410 U/l).Based on the CT, MRI, PET/CT findings a diagnosis of primary hepatic lymphoma was considered more likely than the intrahepatic cholangiocracinoma.Ultrasound guided biopsy of the liver lesion was performed.The histopathological examination and subsequent immunohistochemistry of the liver lesion (Fig. 4; a-h) confirmed the diagnosis of Germinal centre B-cell like Diffuse Large B-cell Lymphoma.

Discussion
Primary Non-Hodgkin's lymphoma of liver is a rare disease (Memeo et al. 1999) with poor prognosis (Freeman et al. 1972).The absence of lymphadenopathy and extrahepatic lesions differentiate it from the secondary hepatic involvement in lymphoproliferative disorders (Patel et al. 2015).Its risk factors include viral infections like HIV, HBV, HCV and EBV (Santos et al. 2003), immunosuppressive therapy (Rostaing et al. 1995) and cirrhosis (Goldin et al. 1993).Its primary treatment remains chemotherapy (Murthy et al. 2000), however surgery, radiotherapy and combined modalities have been documented (Daniel et al. 1985;Pescovitz et al. 1990;Page et al. 2001).On CT, the differential diagnoses include other primary hepatic tumors (hepatocellular carcinoma, cholangiocarcinoma, focal nodular hyperplasia), hepatic metastases and systemic lymphoma.Though literature is limited, a T2 hyperintense lesion with an intense diffusion restriction on MRI and focal or diffuse FDG uptake on PET/CT with absence of other systemic (extra-hepatic) and nodal involvement is documented in few reports (Basheer et al. 2022;Mahajan et al. 2016;Seshadri et al. 2010;Bohlok et al. 2018).The spaceoccupying lesions in the liver that show high metabolic activity on F-18 FDG PET/CT include metastases, lymphoma (systemic), cholangiocarcinoma and poorly differentiated hepatocellular carcinoma or neuroendocrine carcinoma (Rachh and Basu 2014).Differential diagnosis in our case was intrahepatic cholangiocarcinoma due to its multi-focal, hypovascular nature in a non-cirrhotic liver (Seo et al. 2017).However, the absence of biliary dilatation, vascular invasion, capsular retraction with presence of marked diffusion restriction , intense metabolic activity in the liver lesions and normal serum CA19.9 were against this diagnosis.In this case, we highlight the imaging of primary hepatic lymphoma in the differential diagnoses of space-occupying lesions of the liver with normal tumor markers and elevated serum lactate dehydrogenase.(see Figs. 3, 4).

Conclusion
The hybrid F-18 FDG PET/CT is of significant importance in differentiating primary hepatic lymphoma from other primary malignancies of the liver due to its intense metabolic activity.

Fig. 2
Fig. 2 Multiphasic contrast enhanced MRI of liver.(a) Axial T2W image shows a hyperintense lesion (arrow) which depicts marked diffusion restriction on diffusion weighted image (b) and corresponding apparent diffusion coefficient (ADC) map (c) suggesting high cellularity of the lesion.Post-contrast T1W images in (d) early arterial, (e) late arterial, (f ) portal venous, (g) hepatic venous phases show hypoenhancing lesion with mild progressive enhancement of the lesion